Bistable pitch propeller system with bidirectional propeller rotation

ABSTRACT

A propeller includes a blade free to rotate. A first stop is positioned to mechanically engage one or both of a first portion of the blade and a first structure coupled to the blade when the blade is in a first position at a first end of the rotational range of motion. A second stop is positioned to mechanically engage one or both of a second portion of the blade and a second structure coupled to the blade when the blade is in a second position at a second end of the defined rotational range. The blade rotates to the first position against the first stop when the propeller is rotated in a first direction and to the second position against the second stop when the propeller is rotated in a second direction.

BACKGROUND OF THE INVENTION

Rotors (e.g., those used by helicopters) typically are at a single,relatively shallow angle of attack to provide good lift. Propellers(e.g., wing-mounted) typically present a relatively greater angle ofattack to more efficiently propel an aircraft through the air. Althoughsystems exist for varying the pitch of a blade (e.g., so that the samepropeller can switch between an angle of attack which is good forhovering and another which is good for forward flight), such systemstypically use complex mechanical mechanisms that add weight and expense.It would be desirable if new systems could be developed which did notcost as much and/or weight as much.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are disclosed in the followingdetailed description and the accompanying drawings.

FIG. 1 is a diagram illustrating various views of a bistable pitchpropeller embodiment.

FIG. 2 is a state diagram illustrating an embodiment of statesassociated with a bistable pitch propeller.

FIG. 3 is a diagram illustrating an embodiment of an octocopter whichincludes bistable pitch propellers.

FIG. 4A is a diagram illustrating an embodiment of peg stoppers whichstop a peg connected to a bearing.

FIG. 4B is a diagram illustrating an embodiment of a blade stopper whichis designed to come into contact with and stop a blade.

FIG. 5 is a diagram illustrating some embodiments of adjustablestoppers.

FIG. 6 is a diagram illustrating an embodiment of a bistable pitchpropeller, where the blades are configured to return to a restingposition when the propeller is not rotating.

FIG. 7 is a diagram illustrating an embodiment of a blade being held ina feathered blade position using a peg stopper.

FIG. 8 is a flowchart illustrating various embodiments of userinterfaces associated with adjusting the position of a blade.

FIG. 9A is a flowchart illustrating an embodiment of a process toreceive a desired blade pitch from a user interface and adjust theposition of a mechanical stop accordingly.

FIG. 9B is a flowchart illustrating an embodiment of a process toreceive a desired blade pitch from a user interface and adjust theposition of a mechanical stop accordingly where the user interface isdisabled if the mechanical stop is in use.

FIG. 9C is a flowchart illustrating an embodiment of a process toreceive a desired blade pitch from a user interface and adjust theposition of a mechanical stop accordingly where the desired blade pitchis held until the mechanical stop is free.

FIG. 10A is a flowchart illustrating an embodiment of a process toreceive a desired mode from a user interface and adjust the position ofa mechanical stop accordingly.

FIG. 10B is a flowchart illustrating an embodiment of a process toreceive a desired mode from a user interface and adjust the position ofa mechanical stop accordingly where the user interface is disabled ifthe mechanical stop is in use.

FIG. 10C is a flowchart illustrating an embodiment of a process toreceive a desired mode from a user interface and adjust the position ofa mechanical stop accordingly where the desired mode is held until themechanical stop is free.

DETAILED DESCRIPTION

The invention can be implemented in numerous ways, including as aprocess; an apparatus; a system; a composition of matter; a computerprogram product embodied on a computer readable storage medium; and/or aprocessor, such as a processor configured to execute instructions storedon and/or provided by a memory coupled to the processor. In thisspecification, these implementations, or any other form that theinvention may take, may be referred to as techniques. In general, theorder of the steps of disclosed processes may be altered within thescope of the invention. Unless stated otherwise, a component such as aprocessor or a memory described as being configured to perform a taskmay be implemented as a general component that is temporarily configuredto perform the task at a given time or a specific component that ismanufactured to perform the task. As used herein, the term ‘processor’refers to one or more devices, circuits, and/or processing coresconfigured to process data, such as computer program instructions.

A detailed description of one or more embodiments of the invention isprovided below along with accompanying figures that illustrate theprinciples of the invention. The invention is described in connectionwith such embodiments, but the invention is not limited to anyembodiment. The scope of the invention is limited only by the claims andthe invention encompasses numerous alternatives, modifications andequivalents. Numerous specific details are set forth in the followingdescription in order to provide a thorough understanding of theinvention. These details are provided for the purpose of example and theinvention may be practiced according to the claims without some or allof these specific details. For the purpose of clarity, technicalmaterial that is known in the technical fields related to the inventionhas not been described in detail so that the invention is notunnecessarily obscured.

A propeller that is mechanically stable in two (or more) differentpositions depending on a direction of rotation in which the propeller isrotated is disclosed. In various embodiments, a propeller blade of thepropeller system may be mounted so as to be rotatable about an at leastroughly longitudinal axis of the blade. The blade is constructed andmounted such that rotation of the propeller in a first direction ofrotation results in the blade rotating (if/as necessary) about thelongitudinal axis to a first stable position in which a portion of theblade and/or a structure coupled mechanically to the blade engages afirst mechanical stop, resulting in the blade presenting a first angleof attack, while rotation of the propeller in a second (opposite)direction of rotation results in the blade rotating (if/as necessary)about the longitudinal axis to a second stable position in which aportion of the blade and/or a structure coupled mechanically to theblade engages a second mechanical stop, resulting in the bladepresenting a second angle of attack. In some embodiments, aerodynamicforces act on the propeller blade to rotate the blade about itslongitudinal axis to reach and/or maintain the first or second stablestate, as applicable. In some embodiments, other forces (e.g., inaddition to or as an alternative to aerodynamic forces) cause theblade(s) to rotate, such as torque or centripetal force. Although someexamples herein describe aerodynamic force as the force which causes theblades to rotate, this is not intended to be limiting.

FIG. 1 is a diagram illustrating various views of a bistable pitchpropeller embodiment. The bistable pitch propellers described in thisfigure and below are merely exemplary and are not intended to belimiting. For example, although two blades are shown in this figure, anynumber of blades may be employed. Similarly, the shape of the blade(e.g., any washout, the blade thickness, the blade width, any tapering,etc.), the position of the axis of rotation, the position of theaerodynamic center, and the position of the center of mass are merelyexemplary and are not intended to be limiting.

In this example, diagram 100 shows a top view of the exemplary bistablepitch propeller, which in this example has two blades (102). Each bladeis connected to a bearing (104), which permits the blade to rotate aboutan axis of rotation of the blade (106), sometimes referred to as thelongitudinal axis. When the propeller rotates in one direction (e.g.,clockwise from the top view shown in diagram 100), the blades pivot ontheir respective bearings about the axis of rotation of the blade (106).In some embodiments, the blades are relatively lightweight (e.g., tomake rotation of the blades about the axis of rotation easier) and therotation of the propeller causes an aerodynamic force to be applied tothe aerodynamic center (108) of the blade. Since the aerodynamic centeris not on the axis of rotation, the blade rotates when the propellerrotates.

Diagram 112 shows a cross section of one of the blades when that bladeis in a hovering mode or configuration. The rotation of the propellercauses the blade to be pushed because of the aerodynamic force appliedto the blade and the blade's ability to rotate about its longitudinalaxis (106) (e.g., because of the bearing). The aerodynamic force issufficiently strong to push and hold the blade against the first stopper(114), holding the blade in that position and at that pitch (i.e., anangle relative to a plane in which the propeller is being rotated).Diagram 112 thus shows a first blade pitch (or, more generally, bladeposition) at which the pitch propeller is stable in (e.g., the blade isrigid in this position and will not move so long as the propeller isbeing rotated sufficiently).

In diagram 112, the blade pitch is α₁ where α₁ is relatively small. Aflatter blade is therefore presented to the relative wind (shown in thisdiagram going from right to left). This flatter blade pitch providesmore upward thrust and therefore is good for hovering where upwardthrust is desired. For example, α₁ may be defined as 0 degrees, and theblade tip might in that case have a twist angle of 10-20 degrees.Although an aircraft may be able to hover when the blade(s) is/are insome other position (e.g., a forward flight position, as is shown indiagram 116), the blade(s) may be put into this position when theaircraft is hovering in order to improve flight performance and/orreduce noise.

Diagram 116 shows a cross section of one of the blades when thepropeller rotates in the other direction. The rotation of the propellerin this direction causes the blade to flip in the other direction (e.g.,away from the first stopper). As described above, the aerodynamic forcebeing applied to the blade is sufficient to pin or otherwise hold theblade against a second stopper (118). This blade position (pitch) isreferred to as a second blade position (pitch).

In this position, the blade pitch is α₂ where α₂>α₁. The blade pitchpresented to the relative wind (shown in this diagram going from left toright) in this position is therefore steeper. For example, α₂ may bewithin an angular range of 20 to 30 degrees and might therefore have ablade twist that is 30 to 50 degrees at the tip. This steeper bladepitch offers better performance for forward flight, but is not as goodfor hovering, and may in fact stall in hover. The blade pitch (or, moregenerally, blade position) shown in diagram 116 is therefore an exampleof a second blade pitch (or, more generally, blade position) which thepitch propeller is stable in and the blade may be put into this positionwhen the aircraft is in a forward flight mode.

A bistable pitch propeller therefore permits two usable blade pitches(or, more generally, blade positions) using the same propeller and/orblades without requiring electro-mechanical or other structures to drivethe blades to one or the other of the positions. In this particularexample, the two blade positions are associated with and/or optimizedfor hovering and forward flight. Naturally, the blade positions of abistable pitch propeller may be optimized or adjusted for other flightpurposes and/or applications; some examples are described in more detailbelow.

In this example, the center of mass (110) of the blade is on the axis ofrotation of the blade (106). In some other embodiments, the center ofmass does not lie along the axis of rotation. For example, this may bedesirable because inertia will assist in pushing the blade into thefirst blade position or the second blade position (e.g., when thepropeller switches rotational direction).

Some other propellers can be adjusted so that the blades can be in oneof a plurality of blade positions or pitches. However, those propellersystems achieve the different blade positions using hydraulics or othercontrol mechanisms which are (as an example) built into the bladeitself. In contrast, the propeller described herein does not includesuch heavy and expensive hardware, making this propeller designpotentially lighter and less expensive (among other things).

Generally speaking, a propeller per the technique described hereinincludes a blade free to rotate about a longitudinal axis of the bladewithin at least a defined range of motion. A first mechanical stop ispositioned to engage mechanically a first portion of the blade (e.g.,one of the flat sides) and/or a first structure coupled mechanically tothe blade (e.g., a rotatable bearing which is connected to the blade)when the blade is in a first position at a first end of said definedrotational range of motion. A second mechanical stop is positioned toengage mechanically one or both of a second portion of the blade and asecond structure coupled mechanically to the blade when the blade is ina second position at a second end of said defined rotational range ofmotion. An aerodynamic center of the blade lies at a prescribed distancefrom the longitudinal axis of the blade in a direction such thataerodynamic forces act on the blade to rotate the blade tog the firstposition against the first mechanical stop when the propeller is rotatedin a first direction and to rotate the blade to the second positionagainst the second mechanical stop when the propeller is rotated in asecond direction. One example of this is shown in FIG. 1 and otherexamples are described below.

The following figure more formally describes the various statesassociated with rotating the propeller in either direction in order to“pin” the blades of the propeller into one of two (stable) positions.

FIG. 2 is a state diagram illustrating an embodiment of statesassociated with a bistable pitch propeller. In some embodiments, thepropeller instructions (e.g., stop, rotate in a first direction, rotatein a second direction) issued by a flight computer (e.g., implementedusing a processor and memory) cause a bistable pitch propeller to gothrough the states shown.

In state 200, a bistable pitch propeller is stable in a first position.To get into this state, a propeller, which includes a rotatable blade,is rotated in a first direction, wherein the rotation of the propellerin the first direction causes the rotatable blade to be in a first bladeposition. For example, as is shown in FIG. 1, a blade may be able torotate because it is connected to a bearing which is able to rotate. Indiagram 112 in FIG. 1, the rotation of the propeller causes anaerodynamic force to push the blade (102) against the first stopper(114), holding blade (102) in the first blade position shown therein. Inthat example, the blade pitch shown (i.e., α₁) is good for hovering, so(as an example) a propeller may be put into state 200 when the aircraftis hovering or is transitioning to hovering.

In state 202, the bistable pitch propeller is stable in a second state.To get into this state, the propeller is rotated in a second directiondifferent from the first direction, where the rotation of the propellerin the second direction causes the rotatable blade to be in a secondblade position different from the first blade position. See, forexample, diagram 116 in FIG. 1 which shows the blade (102) in a secondblade position. As is shown in FIG. 1, the different blade positionsinclude different blade pitches where α₁≠α₂. The blade position in thisdiagram is better for forward flight and so (as an example) a propellermay be put into state 202 when the aircraft is in forward flight or istransitioning to forward flight.

When the bistable pitch propeller stops, the propeller goes into thestopped state (204), for example because the aerodynamic force caused bythe rotation of the propeller does not push a blade against a firststopper or a second stopper. In some embodiments, a bistable pitchpropeller is designed so that the blades go in to some resting position(e.g., using springs) when the propeller is in stopped state 204.

In addition to switching between hovering and forward flight, anotherexample application is when the propeller is used as a wind turbine. Ifthe wind is too strong, too much electricity may be generated. In oneexample, if the wind is too strong and/or too much electricity is beinggenerated, the propeller will switch directions, causing the blades tobe in a new position (e.g., which “catches” the wind to a lesserdegree), reducing the amount of electricity generated.

The following figure illustrates an example of an aircraft which uses abistable pitch propeller. Naturally, the aircraft shown is merelyexemplary and is not intended to be limiting.

FIG. 3 is a diagram illustrating an embodiment of an octocopter whichincludes bistable pitch propellers. In this particular example, four ofthe octocopter's propellers are bistable pitch propellers and four ofthe octocopter's propellers are not (e.g., those propellers will alwaysrotate in the same direction). Naturally, some other types of aircraftmay be configured differently (e.g., where all of the propellers arebistable pitch propellers and/or some other number of (bistable pitch)propellers are included).

Diagram 300 shows a top view of the octocopter when hovering. From thisview, the directions of rotation for all of the propellers can beobserved. In this mode and for this exemplary aircraft, all of thepropellers are rotating in the same direction (in this example,clockwise).

Diagram 302 shows a side view of the octocopter when hovering. From thisview, it is apparent that the plane of the octocopter (e.g., created bythe four crossbars (304) to which the eight propellers are attached) ishorizontal when hovering. In this mode, it is desirable for thepropellers to be optimized for hovering, and the propellers' directionsof rotation (shown in diagram 300) cause the bistable pitch propellersto have their blades be in a position which is optimized for hovering.

To transition from hovering to forward flight, the octocopter “flips up”so that the plane created by the crossbars (304) is vertical. Forexample, diagram 306 shows a side view of the octocopter in atransitional position where the plane created by the crossbars is at adiagonal. Diagram 308 shows a side view of the octocopter in forwardflight, where the plane created by the crossbars is in a verticalposition. In some embodiments, the octocopter flips up by selectivelyspinning the propellers at different rotational speeds to create a liftdifferential (e.g., the propellers are fixed to the crossbars and theycannot be angled or repositioned). This lift differential causes oneside of the octocopter to flip up (e.g., the left side from the sideviews shown in diagrams 302, 306, and 308.

Diagram 310 shows a top view of the octocopter in forward flight. Asdescribed above, half of the propellers are bistable pitch propellersand the other half are not. In comparing diagram 300 and 310, thebistable pitch propellers can be identified because they are the oneswhich are rotating in different directions. Note, for example, thatpropeller 312 a in diagram 300 and propeller 312 b in diagram 310 arerotating in different directions. Similarly, propeller 316 a and 316 brotate in different directions in diagrams 300 and 310, respectively. Incontrast, propeller 314 a in diagram 300 and propeller 314 b in diagram310 are rotating in the same direction. As shown in this example, insome embodiments, not all of the propellers in an aircraft need to bebistable pitch propellers.

It is noted that the position or mode of the octocopter and propellersare independent and the octocopter can be in one mode (e.g., forwardflight) while the propeller is in the other mode (e.g., hovering). Forexample, in the sequence of diagram 302 to diagram 306 to diagram 308,the propellers may not be switched from hovering mode to forward flightmode until the octocopter has flipped up to a forward flight position(see diagram 308). The blades of the propellers would thereforetemporarily be at an angle that better suited to hovering while theoctocopter is in forward flight position (e.g., at least until theblades of the propellers were switched to the more efficient forwardflight mode). Although the performance may not be optimal (e.g., it maybe noisy or not as efficient), it may still be acceptable.

As described above, a variety of stoppers may be employed and themechanical stopper shown in FIG. 1 is merely one example. The followingfigures illustrate some other examples.

FIG. 4A is a diagram illustrating an embodiment of peg stoppers whichstop a peg connected to a bearing. In the example shown, diagram 400shows a side view of the exemplary peg stoppers. In this example, across section of the blade (e.g., looking towards the nose piece fromthe tip of the blade) is shown with a dashed line (401), where the bladeis attached to the bearing (e.g., extended out of the page). In order toclearly show the peg and peg stoppers, the blade cross section shown inthis figure is transparent. The longitudinal axis of rotation of theblade (also not shown) extends out of the page from the center of thebearing (402). The aerodynamic center of the blade (also not shown) isat a height below the height of the axis of rotation of the blade. Thispermits the bottom portion of the blade to be pushed by an aerodynamicforce either towards the first or second peg stopper, depending upon thepropeller's direction of rotation.

As in the above example(s), bearing 402 is able to rotate. When thebistable pitch propeller is rotated in the direction shown in diagram400 (e.g., counterclockwise when looking down on the nose piece fromabove), an aerodynamic force pushes on the blade (not shown), whichcauses the blade and the bearing to rotate towards the first peg stopper(406). A peg (404) is attached to and radiates outward from the bearing(402) and the bearing rotates until the peg is stopped by the first pegstopper (406). In this example, the peg stoppers are connected to thenose piece (412) so that the peg stoppers can stop the peg from movingfurther, even while the propeller rotates. As is shown in this diagram,the first peg stopper stops the blade at a first blade position (e.g., afirst blade pitch) while the propeller is rotating the direction shown.

Diagram 408 shows the bistable pitch propeller rotating in the oppositedirection. In this direction, an aerodynamic force causes the bearingand peg to rotate towards the second peg stopper (410). The rotation inthis direction is eventually stopped by the second peg stopper (410)forcing the peg to stop. This holds the blade (a cross section of whichis shown with a dashed line) at a second blade position (e.g., a secondblade pitch).

To achieve a desired blade position, a peg stopper is attached to thenose piece to stop the peg at the appropriate position (e.g., to achievea steeper blade angle or a more feathered blade angle). The bladepositions or pitches shown here are merely exemplary and are notintended to be limiting. Some examples are described below where theposition of a stopper is adjustable so that the first blade positionand/or second blade position is/are not necessarily fixed (e.g., the pegstoppers are not welded directly to the nose piece, which would causethem to remain in a fixed position).

Although the peg and bearing are shown here with a seam (e.g., fromwelding or otherwise attaching the peg and bearing together), the pegand bearing may comprise a single piece of metal or other material(e.g., the peg and bearing are cast or cut as a single piece of metal).In various embodiments, a peg and/or a peg stopper may comprise avariety of shapes and/or materials. For example, a peg stopper may bemade of metal (e.g., for strength and/or durability) and have a rubbersleeve or cover (e.g., to cushion the peg which may be pushed forcefullyinto the peg stopper, given the expected high propeller speeds). In someembodiments, a peg stopper has substantially the same height as a peg(e.g., to increase the area where the peg and peg stopper come intocontact which better distributes the pressure and/or to more securelyattach the peg stopper to the nose piece). In some embodiments, the pegand peg stopper have matching surfaces where they come into contact witheach other (e.g., both have a flat surface where they make contact andthe flat surfaces match up) to increase the area where they come intocontact with each other.

The following figure shows a different embodiment where a stopper isdesigned to come into direct contact with the blade (e.g., as opposed tothis figure).

FIG. 4B is a diagram illustrating an embodiment of a blade stopper whichis designed to come into contact with and stop a blade. In the exampleshown, diagram 420 shows a side view when the bistable pitch propelleris rotating in a first direction (e.g., counterclockwise when lookingdown on the nose piece from above). When the propeller is rotating inthis direction, an aerodynamic force pushes against the blade (422),causing the bearing (424) which is attached to the blade to rotate. Therotation of the blade and bearing is stopped when one (e.g.,substantially flat) side of the blade (426) comes into contact with afirst blade stopper (428); this holds the blade in a first bladeposition when the propeller is rotating in the direction shown.

Diagram 432 shows a top view; for clarity, the blade is not shown. As isshown in this view, the first blade stopper (428) and second bladestopper (438) are attached to the nose piece (430), radiating outward sothat it can make contact with the blade (not shown).

Diagram 436 shows a side view when the propeller rotates in the otherdirection (e.g., clockwise when looking down on the nose piece fromabove). In this case, the aerodynamic force causes the blade to bepushed in the other direction, where the blade is stopped by the secondblade stopper (438). In this case, the second side of the blade (434) isin contact with the second blade stopper.

For clarity, the exemplary blade cross section shown here has arelatively simple design or shape but this is not intended to belimiting. A blade used in a real-world embodiment may have a design orshape which is optimized to achieve a variety of design and/orperformance objectives.

In various embodiments, the shape and/or materials(s) of a blade stoppermay vary. For example, the shape of the blade stoppers may beaerodynamic since the propeller is expected to have a relatively highrate of rotation. In some embodiments, a blade stopper is made of metalwith a rubber sleeve or cover.

As described above, in some embodiments, the position of a stopper isadjustable, such that the first blade position and/or the second bladeposition is adjustable. The following figure illustrates some examplesof adjustable stoppers.

FIG. 5 is a diagram illustrating some embodiments of adjustablestoppers. Diagram 500 shows a side view of adjustable peg stoppers. Inthis example, the position of the first peg stopper (502) can bepositioned anywhere within the first cutout (504) and the second pegstopper (506) can be positioned anywhere within the second cutout (508).By adjusting the position of a peg stopper within a cutout, the bladeposition (e.g., when the propeller is rotated and the peg is stopped bythe appropriate peg stopper) can be varied. Naturally, the shape of thecutout (in this example, circular) is merely exemplary and is notintended to be limiting. In some other embodiments, the cutout isL-shaped, vertical, horizontal, diagonal, etc.

In various embodiments, a variety of adjustment mechanisms may be usedin diagram 500. In one example, the peg stoppers are designed to bemanually adjusted, for example, using an exposed knob or using ascrewdriver to turn an exposed screw head. Turning the screw head orknob in turn causes a corresponding peg stopper to move (for example)clockwise/counterclockwise, up/down, left/right within a cutout.

In some embodiments, the nose piece (510) includes actuators whichpermit the automatic (that is, non-manual) adjustment of the firstand/or second peg stoppers within the first and second cutouts,respectively. In one example, when the propeller is not rotating or whenthe peg (512) is stopped by the first peg stopper, the second pegstopper can be moved within the second cutout using the appropriateactuator. Then, when the propeller is rotated in the other direction,the new position of the second peg stopper will cause the blade to stopin a new, second blade position. This permits the propeller to gothrough a sequence of three or more blade positions between takeoff andlanding (e.g., (1) rotate propeller clockwise and blade pitch=α₁, (2)rotate propeller counterclockwise and blade pitch=α₂, (3) adjust firstpeg stopper, (4) rotate propeller clockwise and blade pitch=α₃, etc.).Some examples of user interfaces associated with setting a bladeposition and/or stopper position are described in more detail below.

Diagram 514 illustrates a side view of an example of L-shaped,telescoping blade stoppers. In this example, the first blade stopper(516) and second blade stopper (518) are telescoping, which permits thelength of the blade stoppers to be adjusted. This, in turn, stops theblade at varying blade positions or blade pitches when the propeller isrotated in the appropriate direction. Since a blade will come intocontact with a telescoping blade stopper at a variety of angles (e.g.,depending upon the height of the stopper), the telescoping bladestoppers have rounded ends where the stopper comes into contact with aside of the blade. In some embodiments, some other tip shape is used. Insome embodiments, the end or tip of a telescoping blade stopper isrubberized.

As described above, a variety of mechanisms (e.g., manual adjustmentusing screw(s) and/or knob(s) or automatic adjustment using actuators)may be used to adjust the height of the telescoping blade stoppers. Asdescribed above, in some embodiments the adjustment mechanism is amanual adjustment mechanism and in other embodiments the adjustmentmechanism is an automatic adjustment mechanism.

The ability to adjust the first and/or second blade position may beespecially desirable in wind turbine applications. In wind turbineapplications, the pitch of the blade is adjusted depending upon windstrength. When the wind is too strong and too much electricity is beinggenerated, the pitch of the blade is adjusted so that the blades aremore feathered, reducing the amount of electricity produced. If the winddies down too much, then the pitch of the blade may be adjusted so thatthe blades are at a steeper angle, increasing the amount of electricityproduced.

In some embodiments, the blades of a bistable pitch propeller areconfigured to return to a certain position when the propeller is notrotating. The following figure shows one such example.

FIG. 6 is a diagram illustrating an embodiment of a bistable pitchpropeller, where the blades are configured to return to a restingposition when the propeller is not rotating. In this example, theresting position is a feathered position.

In the example shown, diagram 600 shows the nose piece (602) with twointernal springs (604 a and 604 b). When the propeller is not rotating,there is no aerodynamic force which pushes down the blade (606) towardseither the first mechanical stop or the second mechanical stop (notshown). The first internal spring and second internal spring thereforecollectively push the blade to the center (i.e., a feathered position).In this example, the internal springs are relatively weak such that whenthe propeller is rotating in either direction, the expected aerodynamicforce is greater than the force exerted by the internal springs and theblades can be pushed and held in the first or second blade position.

Diagram 610 shows an interior view of the nose piece. In this diagram,part of the bearing (not shown in diagram 610) is connected to aspring-mounted ball bearing (614). It is noted that the spring-mountedball bearing (614) is different from bearing 612. When the propeller isrotated in a first direction and the blade is in the first bladeposition because of the first peg stopper, the spring-mounted ballbearing is in position 616. When the propeller is rotated in the otherdirection and the blade is in the second blade position because of thesecond peg stopper, the spring-mounted ball bearing is in position 618.When the propeller is not rotating there is no aerodynamic force pushingagainst the blade and so the internal springs shown in diagram 600, aswell as the sloped surface, will cause the spring-mounted ball bearingto come to a rest in position 620 (i.e., the resting, feathered positionwhen the propeller is not rotating). The placement of the “dip” orminima in the sloped surface therefore dictates where the restingposition will be. In this example, the slope(s) (e.g., between positions616, 620, and 618) is/are relatively shallow and the springs arerelatively weak. This permits the expected aerodynamic force to push theblade (e.g., at rest) out of the resting position shown and into thefirst or second blade position when the propeller is rotating.

Naturally, the mechanisms shown here which cause the blade to go to aresting position (in this example, a feathered position) when thepropeller is not rotating are merely exemplary and are not intended tobe limiting. Any (e.g., mechanical) mechanism which returns the blade tosome desired resting position when the propeller is not rotating may beused.

In some cases, it may be desirable to have the feathered blade positionshown here be one of the blade positions created or defined by astopper. The following figure shows an example of this.

FIG. 7 is a diagram illustrating an embodiment of a blade being held ina feathered blade position using a peg stopper. In the example shown, apeg stopper embodiment is shown, but naturally the concepts may beextended to other embodiments. As described above, a bearing (700) whichis able to rotate has a peg (702) attached to it. When the propeller isrotated in the direction shown (e.g., counterclockwise when looking downon the nose piece from above), an aerodynamic force pushes the blade(704) until the peg comes up against the first peg stopper (706) wherethe first peg stopper is connected to the nose piece (708). This causesthe blade to be held at a feathered blade position where α₃=90°. Forexample, if the bistable pitch propeller is being used in a wind turbineapplication, then it may be desirable to have one of the blade positionsdefined or created by a stopper be a feathered blade position. Theblades may be put into this position when the wind is too strong (e.g.,there is a storm) and too much electricity is being generated.

As is shown in FIG. 5, the position of a stopper (and thus a bladeposition when a bistable pitch propeller is rotating) is adjustable insome embodiments. The following figure illustrates some example userinterfaces which may be presented to a pilot or user when there is anautomatic adjustment mechanism (e.g., as opposed to a manualadjustment).

FIG. 8 is a flowchart illustrating various embodiments of userinterfaces associated with adjusting the position of a blade. In someembodiments, the user interface is presented to a pilot or other user bya flight computer (e.g., implemented using a processor and memory) whena stopper has an automatic adjustment mechanism.

User interface 800 shows an example of a user interface where the pilotor user is permitted to specify the desired blade pitches (e.g.,explicitly). To change or otherwise set the first blade pitch, the usercan input a number (in this example, between 0° and 90°) in input box802 a and press the set button (804 a). The flight computer then movesthe adjustable stopper (see, for example, FIG. 5) to a position whichcorresponds to the specified blade pitch. Similarly, a desired bladepitch can be specified for the second blade pitch using input box 802 band set button 804 b.

User interface 806 shows an example of a user interface where the pilotor user selects a flight mode from a plurality of presented flightmodes. In this example, user interface 806 permits the pilot or user toselect a hover mode, a forward flight mode, a wind turbine mode when thewind is weak, a wind turbine mode when the wind is moderate, or a windturbine mode when the wind is strong (i.e., a feathered mode). To setthe first blade position, the desired mode is selected by clicking onthe appropriate radio button and set button 808 a is pressed. Similarly,the second blade position can be set or otherwise adjusted by selectingthe desired mode and pressing set button 808 b. Each flight mode mayhave a corresponding stopper position (e.g., corresponding to a bladepitch which is optimized for that particular mode or application) andthe appropriate stopper is moved to that stopper position.

As described above, in some embodiments an aircraft includes multiplebistable pitch propellers. See, for example, FIG. 3. In suchembodiments, the user interface may include independent controls foreach bistable pitch propeller.

In some embodiments, a given stopper can only be adjusted at certaintimes (e.g., when the propeller is not rotating or when the blade isbeing held in position by the other stopper). If so, this may be handledby the user interface in a variety of ways in various embodiments. Insome embodiments, the user interface does not permit the pilot or userto specify a desired blade pitch or desired mode when a given stoppercannot be adjusted. For example, in user interface 800 and userinterface 806, the affected input box, radio buttons, and/or set buttonmay be disabled and the user may not be able to select those controlsand/or input values into those controls. In some other embodiments, thepilot or user is able to specify a desired blade pitch or desired flightmode at any time, but the user interface informs the pilot or user thatthe change will not be made right away. When the appropriate stopper isable to be adjusted (e.g., because the blade flips over to the otherstopper or the propeller stops rotating), the user interface may beupdated to inform the pilot or user that the change has been made.

The following figures more formally describe how information receivedfrom a user interface may be used to change the position of anadjustable stopper.

FIG. 9A is a flowchart illustrating an embodiment of a process toreceive a desired blade pitch from a user interface and adjust theposition of a mechanical stop accordingly. At 900, a desired blade pitchfor the first position is received from a user interface. See, forexample, user interface 800 in FIG. 8. At 902, a new position for thefirst mechanical stop is determined based at least in part on thedesired blade pitch. For example, there may be some lookup table whichmaps the desired blade pitch to a corresponding position of the stopper.At 904, a position control for the first mechanical stop is set to avalue which corresponds to the new position. For example, a control foran actuator may be set to some value which causes the stopper to bemoved to the new position determined at step 902.

FIG. 9B is a flowchart illustrating an embodiment of a process toreceive a desired blade pitch from a user interface and adjust theposition of a mechanical stop accordingly where the user interface isdisabled if the mechanical stop is in use. For brevity, steps that aresimilar to those described above (e.g., identified by identicalreference numbers) are not discussed in detail here.

At 912, it is determined if a first mechanical stop is in use. Forexample, as described above with respect to FIG. 8, the first mechanicalstop may only be permitted to be moved if the propeller is not rotatingor the second stopper is the one currently holding the blade or peg inplace.

If it is determined that the first mechanical stop is in use at 912,then one or more controls associated with receiving a desired bladepitch for the first position are disabled in a user interface 910. Forexample, in user interface 800 in FIG. 8, a user would not be able toselect and/or input values into input box 802 a or set button 804 a ifthe first mechanical stop is holding the blade in the first bladeposition or pitch. Similarly, in user interface 806, the radio buttonsand set button 808 a may be disabled (e.g., un-selectable) if the firstmechanical stop is holding the blade in the first blade position orpitch. In this example, the process stays in this loop until the firstmechanical stop is no longer in use.

Once (or if) the first mechanical stopper is determined to not be in useat step 912, the controls are enabled at 914. This, for example, permitsthe user to select the previously disabled controls. At 900, the desiredblade pitch for the first position is received from the user interface.At 902, a new position is determined for the first mechanical stop basedat least in part on the desired blade pitch. At 904, a position controlfor the first mechanical stop is set to a value which corresponds to thenew position.

FIG. 9C is a flowchart illustrating an embodiment of a process toreceive a desired blade pitch from a user interface and adjust theposition of a mechanical stop accordingly where the desired blade pitchis held until the mechanical stop is free. As before, steps previouslydescribed are not discussed in detail here for brevity.

At 900, a desired blade pitch for the first position is received from auser interface. At 920, it is determined if a first mechanical stop isin use.

If the first mechanical stop is determined to be in use at 920, amessage indicating that the desired blade pitch will not be immediatelyapplied is displayed at 922. In this example, the process stays in thisloop until the first mechanical stop is no longer in use (e.g., becausethe propeller has stopped rotating or the propeller has switcheddirections of rotation). In this embodiment, the user interface permitsa desired blade pitch to be specified or otherwise input, but then holdson to that pitch without actually making any changes until the relevantmechanical stop is no longer being used to hold or otherwise stop theblade or peg (as an example). In various embodiments, the content of amessage displayed at step 922 may vary. In some embodiments, the messageis fairly simple (e.g., “Waiting”). In some embodiments, the messageidentifies that the wait is due to the stopper being in use (e.g., “Theblade pitch will be changed when the propeller is turned off or thepropeller switches directions.”).

Once (or if) the first mechanical stop is determined to not be in use at920, a new position for the first mechanical stop is determined based atleast in part on the desired blade pitch at 902. In some embodiments, asecond message is displayed to the user, indicating that the desiredblade pitch has been applied (e.g., “Done” or “The blade pitch has beenchanged”).

At 904, a position control for the first mechanical stop is set to avalue which corresponds to the new position.

FIG. 10A is a flowchart illustrating an embodiment of a process toreceive a desired mode from a user interface and adjust the position ofa mechanical stop accordingly. At 1000, a desired mode for the firstposition is received from a user interface, wherein the desired mode isselected from a plurality of modes. See, for example, user interface 806in FIG. 8 where multiple modes are presented and the user selects one.At 1002, a new position is determined for a first mechanical stop basedat least in part on the desired mode. In some embodiments, each possiblemode (e.g., presented to the user) has a corresponding position for themechanical stop pre-determined. In some embodiments, a lookup table isused to map a desired mode to a new mechanical stop position. At 1004, aposition control for the first mechanical stop is set to a value whichcorresponds to the new position. As described above, there may be anactuator to move a peg within a cutout or adjust the height of atelescoping blade stopper, and some control input to the actuator may beset to the appropriate value.

FIG. 10B is a flowchart illustrating an embodiment of a process toreceive a desired mode from a user interface and adjust the position ofa mechanical stop accordingly where the user interface is disabled ifthe mechanical stop is in use. For brevity, steps that have beenpreviously discussed are not discussed in detail here.

At 1012, it is determined if a first mechanical stop is in use. If so,one or more controls associated with receiving a desired mode for thefirst position are disabled in a user interface at 1010. As describedabove, this may include making controls un-selectable and/or notpermitting inputs or other values to be entered. In this example, theprocess stays in this loop until the first stopper is no longer in use.

Once (or if) the first mechanical stop is determined to not be in use atstep 1012, the controls are enabled at 1014. At 1000, the desired modefor the first position is received from the user interface, wherein thedesired mode is selected from a plurality of modes. At 1002, a newposition for the first mechanical stop is determined based at least inpart on the desired mode. At 1004, a position control for the firstmechanical stop is set to a value which corresponds to the new position.

FIG. 10C is a flowchart illustrating an embodiment of a process toreceive a desired mode from a user interface and adjust the position ofa mechanical stop accordingly where the desired mode is held until themechanical stop is free. As before, steps that have been previouslydiscussed are not discussed in detail here for brevity.

At 1000, a desired mode for the first position is received from a userinterface, wherein the desired mode is selected from a plurality ofmodes. At 1020, it is determined if a first mechanical stop is in use.If so, a message indicating that the desired mode will not beimmediately applied is displayed at 1022. As described above, a varietyof messages may be displayed.

Once (or if) it is determined at step 1020 that the first mechanicalstop is no longer in use, a new position is determined for the firstmechanical stop based at least in part on the desired mode at 1002. Insome embodiments, a new or second message is displayed, for exampleindicating that the first mechanical stop has been adjusted to reflectthe desired mode.

At 1004, a position control for the first mechanical stop is set to avalue which corresponds to the new position.

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, the invention is not limitedto the details provided. There are many alternative ways of implementingthe invention. The disclosed embodiments are illustrative and notrestrictive.

What is claimed is:
 1. A propeller, comprising: a blade free to rotate about a longitudinal axis of the blade within at least a defined range of motion; a first mechanical stop positioned to engage mechanically one or both of a first portion of the blade and a first structure coupled mechanically to the blade when the blade is in a first position at a first end of said defined rotational range of motion; and a second mechanical stop positioned to engage mechanically one or both of a second portion of the blade and a second structure coupled mechanically to the blade when the blade is in a second position at a second end of said defined rotational range of motion; wherein the blade rotates to the first position against the first mechanical stop when the propeller is rotated in a first direction and the blade rotates to the second position against the second mechanical stop when the propeller is rotated in a second direction.
 2. The propeller of claim 1, wherein the first structure is the same as the second structure.
 3. The propeller of claim 1, wherein the first position is associated with hovering and the second position is associated with forward flight.
 4. The propeller of claim 1, wherein: the first structure and the second structure are a same rotatable bearing; a peg is connected to the rotatable bearing; the first mechanical stop includes a first peg stopper configured to mechanically stop the peg when the blade is in the first position; and the second mechanical stop includes a second peg stopper configured to mechanically stop the peg when the blade is in the second position.
 5. The propeller of claim 1, wherein: the first structure and the second structure are a same rotatable bearing; a peg is connected to the rotatable bearing; the first mechanical stop includes a first peg stopper configured to mechanically stop the peg when the blade is in the first position; the second mechanical stop includes a second peg stopper configured to mechanically stop the peg when the blade is in the second position; and a position of the first peg stopper is adjustable.
 6. The propeller of claim 1, wherein: the first portion of the blade includes a first side of the blade and the second portion of the blade includes a second side of the blade; the first mechanical stop includes a first blade stopper configured to mechanically stop the first side of the blade when the blade is in the first position; and the second mechanical stop includes a second blade stopper configured to mechanically stop the second side of the blade when the blade is in the second position.
 7. The propeller of claim 1, wherein: the first portion of the blade includes a first side of the blade and the second portion of the blade includes a second side of the blade; the first mechanical stop includes a first blade stopper configured to mechanically stop the first side of the blade when the blade is in the first position; the second mechanical stop includes a second blade stopper configured to mechanically stop the second side of the blade when the blade is in the second position; and a position of the first blade stopper is adjustable.
 8. A method, comprising: receiving, from a user interface, a desired blade pitch for a first position, wherein the desired blade pitch is associated with a propeller which includes: a blade free to rotate about a longitudinal axis of the blade within at least a defined range of motion; a first mechanical stop positioned to engage mechanically one or both of a first portion of the blade and a first structure coupled mechanically to the blade when the blade is in the first position at a first end of said defined rotational range of motion; and a second mechanical stop positioned to engage mechanically one or both of a second portion of the blade and a second structure coupled mechanically to the blade when the blade is in a second position at a second end of said defined rotational range of motion; wherein the blade rotates to the first position against the first mechanical stop when the propeller is rotated in a first direction and the blade rotates to the second position against the second mechanical stop when the propeller is rotated in a second direction; determining a new position for the first mechanical stop based at least in part on the desired blade pitch; and setting a position control for the first mechanical stop to a value which corresponds to the new position.
 9. The method of claim 8 further comprising, prior to receiving the receiving the desired blade pitch for the first position: determining if the first mechanical stop is in use; and in the event it is determined that the first mechanical stop is in use, disabling, in the user interface, one or more controls associated with receiving the desired blade pitch for the first position; and in the event it is determined that the first mechanical stop is not in use, enabling the controls associated with receiving the desired blade pitch for the first position.
 10. The method of claim 8 further comprising, prior to determining the new position for the first mechanical stop: determining if the first mechanical stop is in use; and in the event it is determined that the first mechanical stop is in use, displaying a message indicating the desired blade pitch will not be immediately applied; and in the event it is determined that the first mechanical stop is not in use, determining the new position for the first mechanical stop based at least in part on the desired blade pitch.
 11. A method, comprising: receiving, from a user interface, a desired mode for the first position, wherein the desired mode is selected from a plurality of modes and the desired blade pitch is associated with a propeller which includes: a blade free to rotate about a longitudinal axis of the blade within at least a defined range of motion; a first mechanical stop positioned to engage mechanically one or both of a first portion of the blade and a first structure coupled mechanically to the blade when the blade is in the first position at a first end of said defined rotational range of motion; and a second mechanical stop positioned to engage mechanically one or both of a second portion of the blade and a second structure coupled mechanically to the blade when the blade is in a second position at a second end of said defined rotational range of motion; wherein the blade rotates to the first position against the first mechanical stop when the propeller is rotated in a first direction and the blade rotates to the second position against the second mechanical stop when the propeller is rotated in a second direction; determining a new position for the first mechanical stop based at least in part on the desired mode; and setting a position control for the first mechanical stop to a value which corresponds to the new position.
 12. The method of claim 11 further comprising, prior to receiving the desired mode for the first position: determining if the first mechanical stop is in use; and in the event it is determined that the first mechanical stop is in use, disabling, in the user interface, one or more controls associated with receiving the desired mode for the first position; and in the event it is determined that the first mechanical stop is not in use, enabling the controls associated with receiving the desired mode for the first position.
 13. The method of claim 11 further comprising, prior to determining the new position for the first mechanical stop: determining if the first mechanical stop is in use; and in the event it is determined that the first mechanical stop is in use, displaying a message indicating the desired mode will not be immediately applied; and in the event it is determined that the first mechanical stop is not in use, determine the new position for the first mechanical stop based at least in part on the desired mode. 